A solid-state imaging device is known, which is configured to have effective pixels that output signals based on photoelectric conversion, and reference pixels that output reference signals without photoelectric conversion. The solid-state imaging device reduces noise from an output signal thereof by obtaining a differential signal between a signal output by the effective pixel and the reference signal output by the reference pixel.
In solid-state imaging devices, miniaturization of a pixel size has been advanced to enhance resolution. However, reduction of the area of a photoelectric conversion unit and that of sensitivity of the solid-state imaging device occur with progression of the miniaturization of a pixel size. The solid-state imaging devices are required to proceed with the miniaturization of a pixel size while the reduction of the area of a photoelectric conversion unit is suppressed, to thereby satisfy both of resolution enhancement and suppression of the reduction of sensitivity. Japanese Patent Application Laid-Open No. 2008-271280 discusses a device that performs correlated double sampling (CDS) using plural effective pixels, and configuring a differential pair of an effective pixel and a reference pixel that has properties equivalent to those of each effective pixel except for having no photoelectric conversion function. Each effective pixel stores electric charge output by a photoelectric conversion element and is provided with a floating diffusion capacitor Cfd connected to the gate of an amplifying metal-oxide semiconductor (MOS) transistor. Similarly, each reference pixel stores electric charge and is provided with a floating diffusion capacitor Cfd connected to the gate of an amplifying MOS transistor. In addition, each of the effective pixels and the reference pixels is provided with a capacitor Cio. The capacitor Cio has two terminals, one of which is connected to an output portion of the differential pair, and the other of which is connected to the gate of an amplifying MOS transistor. In the device discussed in Japanese Patent Application Laid-Open No. 2008-271280, the capacitor Cio is very small in capacitance, as compared with the floating diffusion capacitor Cfd. Hereinafter, the capacitor Cio is referred to also as a minute capacitor Cio.
The solid-state imaging device discussed in Japanese Patent Application Laid-Open No. 2008-271280, in which each differential pair is configured by an effective pixel and a reference pixel, may suppress both of a reset noise and a fixed-pattern noise included in each of signals output from the effective pixels and the reference pixels.
Japanese Patent Application Laid-Open No. 2008-271280 discusses a circuit configuration in which each differential pair is configured by an effective pixel and a reference pixel, and in which the amplifying MOS transistors respectively provided in an effective pixel and a reference pixel operate as MOS transistors of an input stage of the differential pair. Accordingly, the amplifying MOS transistor of each of the effective pixels and the reference pixels has a parameter for serving as an amplifying MOS transistor that outputs a signal based on an amount of electric charge stored by the floating diffusion capacitor Cfd, and another parameter for serving as a MOS transistor of the input stage of the differential pair. Thus, it is required to balance the parameter for serving as an amplifying MOS transistor against the parameter for serving as a MOS transistor of the input stage of the differential pair. Accordingly, it is problematic that the flexibility of design is not high.